package lq;

import java.io.BufferedInputStream;
import java.util.Scanner;

public class lq2001 {
        public static void main(String[] args) {
            Scanner s = new Scanner(new BufferedInputStream(System.in));
            double[] d = new double[4];
            while(s.hasNext()) {
                for(int i=0; i<4; ++i)
                    d[i] = s.nextDouble();
                double tp = (d[0]-d[2])*(d[0]-d[2])+(d[1]-d[3])*(d[1]-d[3]);
                double ttp = Math.sqrt(tp);
                System.out.printf("%.2f", ttp);
                System.out.println();
            }
        }


}
